1. Field of the Invention
The present invention relates to an anisotropic conductive sheet which is incorporated into an information apparatus such as a mobile phone, a personal handyphone system (PHS), a personal digital assistant (PDA), or a notebook computer, or an AV apparatus such as a small audio player, and which is used for electrical connection between various components and members, for example, between circuit boards, between a circuit board and an electronic component, or between a conductive portion provided in an exterior component of an apparatus and a circuit board.
2. Description of the Related Art
As shown in FIG. 20, an anisotropic conductive sheet (1) has, within a base portion (2) formed of an insulating elastic sheet, conductive portions (3) continuously extending therethrough in the thickness direction thereof, and exhibits conductivity in the sheet thickness direction of the sheet but exhibits no conductivity in the planar direction of the sheet, that is, exhibiting anisotropy. Electrical connection can be easily effected solely by bringing conductive contacts (4), which are exposed portions of the conductive portions (3), into press contact with the contact portions (electrode portions) of components or members even without employing such means as soldering or mechanical bonding. Further, since the base portion (2) retaining the conductive portions (3) is formed of rubber-like elastic material, it is also possible to absorb vibrations and impact from the outside.
This anisotropic conductive sheet, however, has a problem in that even if positioning is effected between the contacts of the components or members (not shown) and the conductive contacts (4) of the anisotropic conductive sheet (1), positional deviation is liable to occur before the anisotropic conductive sheet (1) has been completely mounted. To solve this problem, there has been proposed, in JP 2000-82512 A, an anisotropic conductive sheet (1a) in which, as shown in FIG. 21, an adhesive layer (5) is provided around the conductive portions (3). With this technique, due to the provision of the adhesive layer (5), when positioning is effected between the contacts of the circuit board and the anisotropic conductive sheet (1a), positional deviation does not easily occur even if some vibration or impact is applied to the anisotropic conductive sheet (1a). Further, even if the positioning is erroneously effected, the sheet can be easily peeled off, thus allowing re-positioning.
However, the anisotropic conductive sheet (1a) has a problem in that, when the sheet (1a) is pressurized at the time of mounting, some adhesive is caused to be squeezed out onto the conductive portions (3) to cover the conductive portions (3), resulting in an increase in conduction resistance.